The present invention relates to the production of microchannel and microcavity systems, and more particularly to an improved method of bonding plane layers together in such production.
Microchannel or microcavity structures are used in inter alia chemical analytical techniques, such as electrophoresis and chromatography. In one type of such microfluidic structures, a channel and/or cavity system is defined between two plane material layers, the recesses which correspond to the channels and cavities, respectively, being formed in one or both of the opposed layer surfaces. The layers are usually bonded together by gluing. Alternatively, if the two layers consist of thermoplastic material, they may be fused together by the application of heat.
When very small channel dimensions are concerned, however, these conventional joining methods tend to deform the channel or cavity system to a great extent by partial clogging with glue or molten material.
The object of the present invention is to overcome this problem by providing a method which permits convenient bonding together of the material layers substantially without obstructing the channel or cavity system.
According to the invention, this is achieved by a method of forming a microchannel and/or microcavity structure by bonding together two elements (1, 2) having opposed plane surfaces of the same or different materials, one or both surfaces having open channels and/or cavities, characterized in that said bonding is effected by applying to one or both element surfaces (1, 2) a thin layer (3) of a solution of a material capable of fusing with and having a lower melting point than that of the material or materials of the two element surfaces (1, 2) in a solvent which substantially does not dissolve the element surface material or materials, removing the solvent, bringing the two elements (1, 2) together, and heating to a temperature where the dissolved material is caused to melt but not the element surface material or materials.
The invention is based on the concept that in order to bond together two planar element surfaces of the same or different materials, preferably thermoplastic, which surfaces when brought together define a channel and/or cavity system between them, there is applied to one or, preferably, both element surfaces a thin layer of another, preferably also thermoplastic, material dissolved in a solvent which does not dissolve the material of the two element surfaces. This dissolved material should, on one hand, be capable of being fused with the material(s) of the two surfaces on which it has been coated, and, on the other hand, melt at a lower temperature than the melting temperature of the element surface material or materials. After evaporation of the solvent, the two surfaces are brought together, e.g. by rolling, whereupon the assembly is heated to a temperature that melts the intermediate (preferably thermoplastic) material but not the material of the element surfaces for effecting joining of the two element surfaces.
The applied solution layer should, of course, have a very small thickness in relation to the width and depth of the channels and microcavities, respectively, which width and depth may be of the order of magnitude of 50 to 100 xcexcm, for example.
When a thermoplastic material is used for the two material surfaces, this thermoplastic material is suitably closely related to the thermoplastic material responsible for the bonding of the channel/cavity structure. As an example of a suitable type of thermoplastic for the present purpose may be mentioned fluoroelastomers.
Suitable combinations of surface/bonding materials and solvents for practising the invention will readily be devised by the person skilled in the art guided by the present description.